1. Field of the Invention
The present invention relates to a recording head usable for carrying out recording on a recording medium (for instance, paper, plastic sheet for OHP (Overhead Projection) or the like) using a specific kind of ink as well as a method of carrying out recording with the use of the aforesaid recording head.
Further, the present invention relates to a recording head and a method of carrying out recording with the use of the head, both of which are usable in image processors, electronic typewriters, facximiles, various kinds of display board or the like.
2. Related Background Art
Among a number of hitherto known recording apparatuses a heat sensitive transferring type recording apparatus has the possibility of using plain papers, and in addition possesses generic features such as small size, light weight, lower noise and others. Accordingly, the heat transfer type recording apparatus has been increasingly put into practical use in recent years.
A method of operating the heat sensitive transferring type recording apparatus as mentioned above is practiced by way of the steps of using an ink film which is coated with heat fusible ink, heating the ink film by means of a recording head to build a certain image pattern, and then transferring the thus fused ink onto a recording medium.
It has been pointed out that the conventional method has problems such as comparatively high operating cost due to the fact that the ink film should be thrown away after completion of usage, and the complicated disposing operation of the used film.
Further, the apparatus of the type using the above-mentioned ink film has problems as mentioned below.
To facilitate understanding of the present invention, a brief description will be provided as to the case where serial printing is effected with the aid of the conventional recording apparatus. As shown in FIG. 2, printing is effected on a recording medium 3 by means of a heated recording head 1 while a carriage 2 is displaced in the direction identified by arrow A. On completion of printing across one line, a platen roller 15 is rotated in the direction identified by arrow B to shift the recording medium 3 by a distance equivalent to one line in the B-direction so that the next printing is initiated.
Incidentally, the recording head 1 for carrying out recording is constructed in such a manner as illustrated in FIG. 3. FIG. 3 is a view as seen in the direction identified by arrow I in FIG. 2. As is apparent from the drawing, seven heating elements 16 are disposed in vertical alignment and a common electrode 17 common to the heating elements 16 is connected to the latter while a signal electrode 18 is connected to each of them. To identify the heating elements 16, symbols C.sub.1, C.sub.2, C.sub.3, C.sub.4, C.sub.5, C.sub.6 and C.sub.7 are used.
When a numeral "7" is printed, a certain intensity of voltage is applied to each of the heating elements 16 in accordance with the time chart shown in FIG. 4. At this moment the carriage 2 is caused to move at a speed of v in the A-direction in FIG. 2. When it is assumed that the applied voltage has a period of t, an electric current supply time is represented by t/2 and a cooling time is represented also by t/2, because the heating elements 16 are heated by application of voltage to them (to effect printing), but there is a necessity for holding a certain period of cooling time until they are heated at the next time by repeated application of voltage to them. FIG. 5 is a time chart illustrating how a heating temperature T of one of the heating elements 16 varies when voltage is continuously applied to it. As is apparent from the drawing, temperature increases gradually to reach the highest point Ts, as long as voltage is applied, and when the application of voltage is interrupted, the temperature decreases gradually to reach the initial temperature To. Thus, the increase and decrease of temperature are repeated in the above-described manner in accordance with the ON-OFF condition of the voltage.
Referring to FIG. 4, at the time of t.sub.1 voltage is applied only to C.sub.1 among the heating elements 16, at the next time of t.sub.2 voltage is applied to C.sub.1, C.sub.5, C.sub.6 and C.sub.7, at the next time of t.sub.3 voltage is applied to C.sub.1 and C.sub.4, at the next time of t.sub.4 voltage is applied to C.sub.1 and C.sub.3, and at the next time of t.sub.5 voltage is applied to C.sub.1 and C.sub.2 whereby a numeral "7" as shown in FIG. 6 is printed.
However, due to the fact that there is a necessity for cooling the heating elements 16 for a certain period of time as mentioned above, it is not easy to effect printing at a higher speed. If a moving speed v of the carriage is increased twice and a frequency of voltage application is reduced to a half of the normal one t, as shown in FIGS. 7 to 9, one of the heating elements 16 has the a maximum temperature of Ts/2 such that voltage is continuously applied to it, because the period of time of voltage application is reduced to t/4, as shown in FIG. 7. As a result, there occurs a shortage in the amount of generated heat, causing printing to be achieved at a lower visual density as shown in FIG. 8. Obviously, this is not desirable.
Further, if the carriage is caused to move at a moving speed two times as high as the normal moving speed v, but a voltage application period is set equal to the normal voltage application period t, as shown in FIGS. 10 to 12, each of the heating elements 16 reaches the highest heating temperature Ts just like in the normal operative state as shown in FIG. 11, because voltage is applied to the heating elements 16 for the same period of time t/2 as in the normal operative state. However, due to the fact that the moving speed of the carriage is set to 2v, printing is achieved with an open space produced between the adjacent printed dots as shown in FIG. 12. As a result, the whole printed image exhibits an elongation in the transverse direction.
To obviate the foregoing problems as pointed out with respect to the conventional recording apparatus, there is a proposal as to a recording method as shown in FIG. 1. For practicing the proposed method, a recording head 1 usable for heat sensitive recording includes a heating member 1d having an ink passage hole 1f formed therein through which ink passes. Semisolid ink is contained in an ink container and when the heating member 1d generates heat, ink existent in the vicinity of the heating member 1d reduces its viscosity whereby it flows through the passage hole 1f under the effect of pressure exerted in the ink container in the direction toward the passage hole 1f. In practice, the recording head is so constructed that a plurality of ink passage holes 1f are arranged in an array-shape and an ink image is built on a recording medium 3 in response to heating signals selectively transmitted to heating members 1d allocated to the corresponding passage holes 1f through which softened ink flows to the outside.
The proposed method has advantageous features that there is no necessity for ink film, and a high efficiency is obtainable in respect of thermal energy because ink is directly heated without using any type of film.
The present invention has been made as a result of further development work conducted in connection with the above-mentioned conventional recording method.